Aim: The standard dosage recommendations for beta-lactam antibiotics can result in very low drug levels in intensive care (IC) patients and burn patients in the absence of renal dysfunction. We studied the pharmacokinetic parameters and serum concentrations of ceftazidime (CF) and cefepime (CE) in burn patients and analyzed the modifications according to clinical and biological parameters and in particular age and creatinine clearance.
Material and methods: Two pharmacokinetic studies were carried out with daily doses of 1 g x 6 for CF (n = 17) and 2 g x 3 for CE (n = 13). Creatinine clearance (CL(CR)) was both estimated and measured. Blood was sampled at steady state after an initial and a subsequent antibiotic dose. C(max) (maximal) and C(min) (minimal) concentrations were measured by HPLC. The influence of clinical and biological data was analyzed using ANOVA, ANCOVA and stepwise multiple linear regression.
Results: The ratio of C(min) to the low MIC break point (4 mg/l) was lower than 4 in 52% of subjects receiving CF and in 80% of subjects receiving CE. The C(min) of CF was correlated with measured CL(CR) and was higher in mechanically ventilated patients than in non-ventilated patients. The clearance of CF was correlated with age. The C(min) of CE was correlated with age and drug clearance with measured CL(CR). Therefore dosage adjustment of these drugs in burn patients needs to take into account age, measured creatinine clearance and the danger of low concentrations occurring when the creatinine clearance is greater than 120 ml x min(-1).
Conclusion: In burn patients, the pharmacokinetic disposition of CF and CE was much more variable than in healthy subjects. Age and CL(CR) were predictors of the disposition of these antibiotics. Shortening the dosage interval or using continuous infusions will prevent low serum levels and keep trough levels above the MIC for longer periods of time. In view of the lack of a bedside measurement technique for ceftazidime and cefepime levels, we suggest a more frequent use of measured CL(CR) in order to attain efficacious clinical concentrations.